1. Field of the Invention
The present invention relates to data filtering, and more particularly, to a signal adaptive filtering method for reducing a blocking effect and ringing noise, and a signal adaptive filter suitable for the method.
2. Description of the Related Art
Generally, picture encoding standards such as the Motion Picture Expert Groups (MPEG) of the International Organization for Standardization (ISO) and H.263 recommended by the International Telecommunication Union (ITU) adopt block-based motion estimation and discrete cosine transform (DCT) compression of blocks. When an image is highly compressed the block-based coding may cause a blocking effect and ringing noise, as is well known. A typical blocking effect is grid noise in a homogeneous area in which adjacent pixels have relatively similar pixel values. Another blocking effect is staircase noise which has the shape of a staircase and is generated along an edge of the image. Also, the ringing noise is due to the typical Gibb's phenomenon which results from truncation of a DCT coefficient during quantization when the image is highly compressed.
In the case of grid noise, traces caused by the process being performed on each block can be seen at the boundary between blocks when the compressed data is restored to be displayed on a screen. Accordingly, a border between blocks can be noticed by a user. In the case of staircase noise, an edge of the image is shaped like a staircase, so that a jagged edge of the image can be noticed by a user. The ringing noise causes a problem in that an object in the image is displayed as multiple overlapping objects.